Tuberculosis remains a critical global health problem. The long-term objective of this project is to better understand Mycobacterium tuberculosis'(Mtb) physiological response to host-associated environmental conditions, so that effective strategies can be developed to prevent and/or treat Mtb infection. Carbon dioxide is an essential virulence-associated environmental signal for many bacterial pathogens within their host environments, but its effects on Mtb have not been rigorously examined. Recent studies showed that physiologic levels of carbon dioxide completely abrogate hypoxia-induced growth arrest in TB complex bacteria. These findings challenge the in vivo significance of the Mtb 'hypoxia-induced growth arrest'model, because carbon dioxide is abundant in most areas within the host. The goal of this exploratory project is to identify CO2-associated effects on Mtb gene regulation and metabolism, including those that may facilitate Mtb's transition to non-replicating persistence. Specific aims include: Aim 1: identification of CO2-associated effects on Mtb gene expression, using proteomic and RNA expression-based microarray approaches; Aim 2: evaluation of CO2-associated effects on Mtb's intracellular pH and carbon pathway utilization, using genetic and biochemical approaches. This work will explore new insights regarding conditions that may affect Mtb's metabolic state within the host, with the potential to identify new targets for TB vaccines, therapeutics, and/ or diagnostic purposes. Characterization of Mtb's physiological response to carbon dioxide will broaden our understanding of the tubercle bacillus'response to a critical environmental condition that will be encountered within the host, and provide information on factors that may affect the establishment of tuberculosis infection, persistence and/or disease. Tuberculosis, caused by Mtb, remains a serious global public health problem. Characterization of Mtb's physiological response to carbon dioxide will broaden our understanding of the tubercle bacillus'response to a critical environmental condition that will be encountered within the host, with the potential to identify new targets for TB vaccines, therapeutics, and/ or diagnostic purposes.